The invention relates to a flat gasket, e.g. a cylinder head gasket for an internal combustion engine, as well as to a process for its production, with at least one through opening provided with a metallic border resting on the opening edge and having a U-shaped cross-section and treated with an impregnating agent solution.
Such gaskets are frequently produced from a soft material on a sheet metal carrier. The gasket material must deform to such an extent under the sealing pressure that on fitting, the adaptation to the sealing faces necessary for sealing is obtained. When used as a cylinder head gasket, the metal border has the function of shielding the soft material against the very hot combustion gases. It must also provide a seal against the gases which are under a high pressure. The cross-sectionally U-shaped borders bent over the opening edge or rim serve to produce a locally increased surface compression for sealing against the high combustion chamber pressures. As is known, in the combustion chamber area much higher pressures are required than in the case of sealing oil and coolants.
In order to ensure an adequate microsealing and macrosealing during the first starting revolutions of a new internal combustion engine the surfaces of the border facing the engine block and cylinder head are covered with elastomeric coatings, which have to be applied in complicated, separate operations. Their basic composition often comprises a silicone-based elastomer, which crosslinks under heat action. The impregnating agents used for treating the flat gasket after stamping and bordering have a similar composition and serve as binders.
A simultaneous coating of the border and impregnation of the soft material has hitherto failed in that during the dripping process following impregnation, uncontrolled residual drip formation and accumulations on the smooth metal surface of the border are unavoidable. Therefore separate cleaning operations for the border are required, in order to obtain a clean surface as a base for a uniform coating thickness of the following elastomer coating. As the cleaning process requires both the dissolving of the accumulations in a solvent and a reliable wiping off, this operation involves relatively high costs.